The task was as a team to create a gripper that could pick up, swing, and set back in the same position an object. This object was made out of aluminum, was the shape of a large fidget spinner, and weighed ~1.11 kg. Some specifications included that the gripper could not interfere with the support structure underneath the fidget spinner, nor can it touch the bottom of the fidget spinner. For testing the gripper will be attached to a swinging arm with a drive shaft and it will be moved into place along the same path as it will swing along. The gripper must somehow use the actuation provided by the drive shaft to hold the fidget spinner. When the motor is on, it will drive the shaft with medium speed when unloaded or medium torque when stalled.
Design Description and Rationale:
Our design features acrylic for lightness, three arms which together act as clamps, and vertical supports that connect each arm to the base. The arms are attached to a triangular plate which mounts to the stand. One spring is attached to each corner of the triangle, with the other end connected to its respective arm underneath. These hold the arms up in a retracted position. String is attached to the shaft and connects to the hinged lower part of the arms so that when the motor turns, the string will be pulled taught and the gripper will close (into the position shown above). The strings are braided together to keep the distances of travel the same. Another string is also attached to the drive shaft to limit rotation when the motor is back-driven.
Because we cannot contact the object underneath, we determined the best action is to pick up the object by clamping against the sides. There are three arms equally spaced 120 degrees from each other to clamp the fidget spinner on the inner concave regions. At the end of the arms are Dycem pads that will allow the artifact to be held securely with friction forces from clamping. To mitigate bending in the vertical supports when the artifact is gripped, we have a triangular plate which braces the supports. This increases member stiffness and saves more weight than if a stiffer, but heavier, material was used to manufacture the supports.